Abstract

The conservation of angular momentum during the interactions of sound fields with objects is associated with the symmetry in the fields and the objects. Simple arguments of symmetry and/or conservation can have efficient applications in analyses of angular momentum transfer during the interactions. Scenarios that will be illustrated include: (a) conserved phase distribution for analysis of torques exerted by vortex beams on axis-symmetric objects for its connection with absorption [L. Zhang and P. L. Marston, JASA 129, 1679–1680 (2011); Phys. Rev. E. 84, 065601 (2011)], (b) symmetric superposition of vortex beams for analysis of torques exerted by orthogonal waves on a small compressible object in a slightly viscous fluid [L. Zhang and P. L. Marston, JASA 136, 2917–2921 (2014)], and (c) broken symmetry in a planar meta-screen for introducing angular momentum into a plane sound field of null angular momentum [Y. Li et al., Phys. Rev. Appl. 4, 024003 (2015); X. Jiang et al., in preparation].